Inbreeding avoidance mechanism : how premating conditions may influence the mating system in a quasi-gregarious parasitoid of aphids, Aphidius matricariae
(2012)
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- Authors
- Supervisors
- Hance, Thierry
- Abstract
- (en) The theory of sexual selection was formulated by Darwin (1871) to explain the origin of sexually dimorphic traits that are detrimental to survival. He believed that sexual selection arises from either mate choice or intra-sexual competition for mates, reasoning that such traits could evolve if they conferred a fitness advantage on their bearer. It is well conceded that males and females do not mate randomly and that mate choice is an important aspect of mating systems. Mate choice can operate on numerous traits but inbreeding avoidance is one of the major aspects that drive mate choice, from plants to society-living animals. Indeed, many species suffer from inbreeding depression and had selected inbreeding avoidance strategies: dispersal, favouring extra-pair or extra-group copulation, recognition and avoidance of kin as mate, delayed maturation, role of the social system, etc. However optimal mate choice can also be constrained by mate availability and environmental or physiological factors. Little data are currently available on the different steps preceding the mating itself for males and females such as the place of emergence of both sex at adulthood, the probability to meet a kin in its immediate environment and how these factors may influence the final choice. It is particularly the case for Hymenoptera parasitoids, where adult emergence is constrained by the host behaviour. Parasitoids are organisms that parasite others and kill them as a result of their development. Hymenoptera parasitoids are haplo-diploid organisms and for some groups, like aphid parasitoids (Aphidiinae: Braconidae), when a female mate with a related male, the single-locus Complementary Sex Determination mechanism may lead to the production of unfertile diploid males. Moreover, in the case of aphid parasitoids, as their host lives in groups, when a female laid its eggs in an aphid colony, a synchronous emergence of its offspring may results in Local Mate Competition. Thus, aphid parasitoids have probably developed some mechanisms to avoid mating between siblings or competition between brothers. For the Aphidiinae subfamily few studies address the consequences of inbreeding and their actual status of semi-gegarious species. In that context, our hypothesis is first that aphid behaviour after parasitism may influence the parasitoid mating structure, secondly that aphid parasitoids have developed adapatations to avoid inbreeding and Local Mate Competition. We show that the peach potato aphid Myzus persicae disperses from its colony when disturbed by a parasitoid female Aphidius matricariae. This induces the solitary emergence of the offspring (paper 1). We then observe that the spatio-temporal emergence pattern of Aphidius matricariae adults could lower the probability to encounter a sib. Indeed, we demonstrate the existence of protandry and that the distribution of males and females emergence from a single brood spreads over 3 days (paper 2). Brothers and sisters do not often emerge at the same time, increasing the probability of outbreeding (paper 2). Then, our second objective was to evaluate what were the traits related to mating that could favour outbreeding. The hypothesis of a differential mating window is validated: females need around 30 minutes to be receptive to males and accept to mate until they are 6 days old (paper 4). Males are sexually mature just after emergence and are capable to court and mate female during 11 days in lab conditions (paper 4). Contrary to our predictions, females usually mate only once (paper 3) and no behavioural avoidance of mating between brothers and sisters (paper 5) occur. This is probably due to the previous traits that decreased the sib mating probabilities enough to have a low rate of inbreeding in natural populations. To conclude, A. matricariae exhibit different life-history strategies and mating behaviours that result in a decrease of the inbreeding probability in lab conditions. Field studies and precise sex ratio evaluations are needed to confirm and refine our observations.
- Affiliations
UCLouvain SST/ELI/ELIB - Biodiversity
Citations
Bourdais, D. (2012). Inbreeding avoidance mechanism : how premating conditions may influence the mating system in a quasi-gregarious parasitoid of aphids, Aphidius matricariae. https://hdl.handle.net/2078.5/158968